If we’re talking the Magpul MOEs, all polymer, they’re fine.
No, they won’t last as long as a steel or steel reinforced mag, but they’re usually easy to find for cheap, they’re available in 20 rounders (which is why I have some) and they do feed a bit higher than any surplus mags I own. They also seem to fit just about everything.
Got some of the first gen AC Unity mags too, I think mine were $8 a pop. For that price they’re great. Unlike the upgraded gen 2 Magpuls, they’re reinforced front AND back. Never understood why Magpul charges almost twice as much for the gen 2 over the all poly MOE and only reinforced one end. I heard the Magpul gen 2s were spec’d a bit larger so they’re a tighter fit bs MOEs.
The Unitys are more flexible on the side than Magpuls when unloaded.
I still shoot a lot of corrosive ammo so I run that thru my Magpuls, Tapcos, Unitys & Korean mags and save the non-corrosive for surplus mags.